Outline of IPB IDC Slots
74F899QC 9-bit Latchable Transceiver with Parity Generator-Checker
TI SN75176B Differential Bus Transceivers
SWAG: These might take SE output from the 53C700s and convert it to Differential.
NCR 53C700 SCSI I/O Processor Data Manual, Feb 1990
NCR 53C700 SCSI I/O Processor Data Manual, Nov 1992
NCR 53C700 SCSI I/O Processor Programmers Guide, Mar 1990
Channel A and B pads only
D1-2 Activity LEDs (green)
D3 Diagnostics LED (red)
J1 SCSI Port A
J2 SCSI Port B
Resistor SIPPs (lower right) unknown purpose, socketed
External SCSI Port Mounting
For some odd reason, the HPDB-50 ports have
the usual catches for a HPDB-50 SCSI cable to latch on to.
But oddly enough, there are short hex mounting posts,
similar to those used with parallel or serial ports. These
hex posts are right up against the HPDB-50 port catches,
and would prevent anyone from using the pretty good cable
connectors that clip on to the SCSI port.
3 Extra 74F899QC?
There are 16 74F899QC 9-Bit Latchable Transceiver with
Parity Generator-Checkers on the IDC, compared with 13
on the other IPB cards. My SWAG is they have to do with
the synchronization of the Orthogonal RAID function?
Select SE or Differential with PCBs
Parallan did some innovative design. Each 53C700 can be
configured to feed SE or Differential signals to the
external SCSI ports. There are three female headers per
53C700 on the IDC. There is a PCB with two male headers.
To choose SE or Differential, simply move the PCB to
select the SCSI mode.
Note the silkscreened "Single Ended" and "Differential"
between the 50 pin headers.
This image shows the configuration for SE drives.
Now, I am familiar with the term pack on a SCSI/A
needing to be removed if there are SCSI devices on the
External -AND- Internal ports. So how does one remove
the term resistors in this case? Some fiddly bit of work
pulling these SIPPs out, quite cramped if you want to
pull the three SE SIPPs out...
SE and Differential
SE and Diff Terminating
The three orange resistor SIPPs (4608R-104-221/331)
closest to the top of the lower 50 pin header are the
terminating resistors for SE mode. The FOUR red
resistor SIPPs (L101C331 246) -AND- the three orange
DIPs (4114R-001-151) below them are the terminating
resistors for Differential mode.
(Ed. Image typo, should be
Note: Pin 1 on the
SIPPs and DIPs are to the right!
Note: There is only
ONE PTC (F1) between both SCSI headers.
Disks, Controllers & Bays
Two independent (dual channel) RISC-based SCSI
I/II controllers on single card; 64 bit interface to
IP-Bus. The sales stuff refers to 5MB/s versions of the
53C700, the 1990 version of the datasheet says 5MB/s,
but that same datasheet also mentions that there was a
planned 10MB/s improvement. The 53C700 on the IDC are
date stamped 9245. Period ads mention synchronous rates
of roughly 6.75 to 9.75 MB/s. So... how fast is it?
To run Orthogonal RAID, you need two IDCs, so there are
four NCR 53C700 (2 per IDC). Both 53C700s on an IDC are
fed from a 25.000000 MHz oscillator. No fooling, six
places to the right. With normal RAID, all of the drives
are on one controller, (all use one clock), but 2
independent IDCs NEED a very precise clock on-board to
enable them to synchronize.
Note: The 53C700
has a "SCRIPTS" processor, which is the "RISC-based"
controller. There is no separate RISC chip on the IDC.
"Factory" disks are the IBM 0661-467 (400 MB) and 0663
(1 GB) SCSI disks. The 295 does check the HD firmware
for a text string.
Supports 1 to 28 hot insertion/extraction disks (all
The removable trays are CRU DataPort I trays, which are
Max of 9 GB internally (9 bays x 1 GB disk).
Max of 28 GB total (4 ) 53C700 x 7 disks (1GB) with
Ten 3.5" half height bays internally (diskette uses
one). That leaves 9 bays, with one for the system
disk, leaves 8 drive bays to support Orthogonal RAID-5
(with on-line spares). So without the SCSI expansion
chassis, this limits one to 8 drives (two SCSI drives
connected to each 53C700). I suppose you could run one
SCSI drive on each 53C700 for the smallest OR-5
footprint, but you won't have the on-line spares to
support automatic RAID array rebuilding...
Supports 1 to 3 optional External Expansion Cabinets
each with ten 5.25" half height or five 5.25" full
OS/2 preload includes FTUTIL: allows disk pairs to be
striped, mirrored, or duplexed. Also allows hot spare
pooling, hot insertion/extraction, automatic data
rebuild, and hot fix.
The disks in the PS/2 Servers 195/295 can either be used
as individual disks, configured as hot-standby spare
disks, configured as Parallel Disk Array (PDA) pairs
using the FTAUTIL.EXE standard utility, or combined into
RAID-5 PDAs using the optional Orthogonal RAID-5 Disk
Array/2 software, which implements orthogonal RAID-5
fault tolerance. Data and parity information are spread
across the disks in a PDA, thus both protecting the data
and providing performance improvements for applications
which mainly read data (rather than write data).
The PDA can be set up to be "orthogonal" by ensuring
that the disks of the array are on separate disk
controllers, thus increasing the availability of the
system still further.
One or two disk controllers can be
installed on the IP-Bus, providing two or four SCSI disk
channels, respectively. Each channel can support up to
seven SCSI disks, for a maximum of 28 disk drives.
When all four disk channels are available, then arrays can be
configured across multiple SCSI channels. SCSI channels
are defined vertically, arrays can be defined
horizontally, thus giving an "orthogonal" configuration.
This provides extra fault-tolerance (since a single SCSI
disk channel, a single cable, or a single disk can fail
without losing the array).
PDAs are set up using the Server 295 reference
diskette. Information on the PDAs can be displayed
using MASS/2. Configuring spare drives and
reconstructing a PDA following a drive failure is done
using the utility PDAUTIL, as well as automatically by
MASS/2, if there is a hot-standby spare disk in the
The PS/2 Server 195/295 uses Orthogonal RAID-5, an
enhancement on RAID-5.
The minimum full Orthogonal RAID-5 array is eight
drives. Four for data, and four for online spares,
Multiple requests to one disk or across one adapter
will typically take longer to satisfy than the same
number of requests to multiple disks across multiple
adapters. A standard RAID-5 system depends on just one
disk adapter which all of the disks are connected.
Orthogonal RAID-5 Disk Array technology removes these
bottlenecks, and provides an extremely high level of
reliability. Unlike previous RAID-5
implementations, the Orthogonal RAID-5 Disk Array
provides redundant SCSI-adapters, SCSI buses, power
supplies, power cables and fan assemblies. By
multiplexing data access across all four SCSI
controllers, the Orthogonal RAID-5 also significantly
improves data access performance.
Any one component of a Orthogonal RAID-5 disk subsystem
can fail with no loss of data and no interruption to
RAID Level Performance Characteristics
||High I/O Rate
1) The MTBF for single disks can range from 10,000 to 800,000 hours.
2) Availability = MTBF of one disk divided by the number of disks in the array.